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  Reply # 2108727 16-Oct-2018 11:17
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SaltyNZ:

 

Geektastic:

 

mattwnz:

 

The bigger problem with petrol price rises, is the knock on effects with everything going up in price, as everything has to be transported. It seems for a long time everyone wanted the NZ dollar to weaken, so NZ would earn more for their exports, such as milk. Now it has gone weaker, it means imports are now higher, including fuel. There is no way to keep everyone happy. 

 

 

 

 

Indeed. This is one reason why many things are much cheaper in the USA, where they don't use petrol as a source of government revenue to such a vast extent as Europe and here.

 

 

 

 

They don't use anything as a source of government revenue. That's why their debts are in the tens of trillions of dollars and climbing every day.

 

 

 

 

no Govt revenues?  well I wish I paid 0% US federal tax, but I don't.

 

 


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  Reply # 2108758 16-Oct-2018 11:53
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nathan:

 

 

 

no Govt revenues?  well I wish I paid 0% US federal tax, but I don't.

 

 

 

 

 

 

Well, that's your own fault for not being a billionaire. Git gud.





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  Reply # 2108822 16-Oct-2018 12:52
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Aredwood:Except that there will be a balance point, at which going slower won't actually reduce your fuel usage. And which in fact will cause you to use extra fuel.

If driving slower means that the gearbox has to run in a lower gear, or the lockup clutch has to disengage. You will almost certainly be using more fuel, despite going slower.

On a lot of diesel cars and older petrol cars. They typically have only a narrow RPM band where the engine operates at peak efficiency. So the most efficient speed will typically be whatever speed keeps the engine in that band while in top gear.

 

Cars are rarely driven at peak engine efficiency.

 

Peak efficiency of an ICE is at wide-open-throttle, with RPM between max torque (typically about 3,000) and max power (typically about 5,000 RPM). So, you would only achieve peak engine efficiency if you were climbing a very steep hill in a very low-powered car (e.g. a 1948 Morris Minor on that steep hill out of Te Kuiti) or doing 150kph or so in a modern car. The downside of running at peak engine efficiency is that every hill or puff of headwind would decrease your speed and engine power, and you would have no way to get back up to speed without compromising efficiency. Conversely, a slight downhill would see engine RPMs increasing, so the driver has to close the throttle somewhat, making the engine inefficient again. A smaller engine in a car uses less fuel because the engine is runnging closer to peak efficiency more of the time.

 

A large amount of energy is used by the engine to move air from the inlet to the exhaust. A lot of energy is also sent out the exhaust pipe and radiator as heat. So, at best, an ICE is at best about 35% efficient at turning potential energy in its fuel into useful work. Motor manufacturers have come up with a whole lot of clever things (e.g. variable valve & ignition timing, turbo-charging, computer-controlled fuel injection)  to reduce the inefficiency of IC engines at typical open-road RPM.

 

Drag increases exponentially (square? or cube?) with speed. So, at higher speeds, your engine is running maybe 10% more efficiently, but you are using maybe 30% more energy to overcome drag. In normal driving, most of the "aerodynamics" on modern cars don't do anything except increase drag.

 

 


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  Reply # 2109037 16-Oct-2018 17:49
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frankv:

Aredwood:Except that there will be a balance point, at which going slower won't actually reduce your fuel usage. And which in fact will cause you to use extra fuel.

If driving slower means that the gearbox has to run in a lower gear, or the lockup clutch has to disengage. You will almost certainly be using more fuel, despite going slower.

On a lot of diesel cars and older petrol cars. They typically have only a narrow RPM band where the engine operates at peak efficiency. So the most efficient speed will typically be whatever speed keeps the engine in that band while in top gear.


Cars are rarely driven at peak engine efficiency.


Peak efficiency of an ICE is at wide-open-throttle, with RPM between max torque (typically about 3,000) and max power (typically about 5,000 RPM). So, you would only achieve peak engine efficiency if you were climbing a very steep hill in a very low-powered car (e.g. a 1948 Morris Minor on that steep hill out of Te Kuiti) or doing 150kph or so in a modern car. The downside of running at peak engine efficiency is that every hill or puff of headwind would decrease your speed and engine power, and you would have no way to get back up to speed without compromising efficiency. Conversely, a slight downhill would see engine RPMs increasing, so the driver has to close the throttle somewhat, making the engine inefficient again. A smaller engine in a car uses less fuel because the engine is runnging closer to peak efficiency more of the time.


A large amount of energy is used by the engine to move air from the inlet to the exhaust. A lot of energy is also sent out the exhaust pipe and radiator as heat. So, at best, an ICE is at best about 35% efficient at turning potential energy in its fuel into useful work. Motor manufacturers have come up with a whole lot of clever things (e.g. variable valve & ignition timing, turbo-charging, computer-controlled fuel injection)  to reduce the inefficiency of IC engines at typical open-road RPM.


Drag increases exponentially (square? or cube?) with speed. So, at higher speeds, your engine is running maybe 10% more efficiently, but you are using maybe 30% more energy to overcome drag. In normal driving, most of the "aerodynamics" on modern cars don't do anything except increase drag.


 



The ECU or carburetor runs the engine slightly rich at full throttle. And ignition advance is normally less at full throttle compared to part throttle. Those 2 things alone make an engine less efficient on a basis of fuel usage Vs power output. But this is not normally a problem as you want max power at full throttle.

The only benefit of full throttle Vs part throttle is that you have a lower equivalent compression ratio when there is less than atmospheric pressure in the inlet manifold. But the higher the air pressure in the inlet manifold, the more fuel has to be injected to keep the air / fuel ratio correct. Even if an engine is slightly more efficient at full throttle, it won't be double or more than double efficient compared to half throttle.

Things like valve timing, intake manifold and exhaust manifold runner lengths and diameters, exhaust pipe diameter, etc are optimized for a certain RPM and average engine load. The exhaust gasses have momentum, so a partly restrictive exhaust pipe helps to "suck" the last bit of exhaust out of the cylinders at the end of the exhaust stroke. And it is also why putting a larger exhaust on an NA car often kills the low end torque. Even when you gain more top end power. It would be very rare that you would need or want full throttle at 3000rpm on an engine that could most likely handle 7000rpm. As if you want max power, you would change down the gears.

If engines really were more efficient at full throttle, it would be possible to save fuel by driving around at full throttle constantly. While also pressing the brake to keep the car at a steady speed.





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  Reply # 2109060 16-Oct-2018 18:45
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MileHighKiwi: The rising cost of petrol is one of the main reasons we recently bought a diesel (2014 Mazda CX-5 2.2L turbo diesel). $85 to fill up compared to $130 in our Mazda 6 (95 petrol). Even with RUC I estimate we'll be about $1k better off per year.

 

 

 

It will be interesting to see how you get on. I've been doing my maths on diesel vs petrol and basically need the diesel to be about 0.5L better per 100km to cost less than my current car. That doesn't take into account servicing however. 

 

And in theory diesels tend to get closer to their stated mileage than petrol. However my comparisons are on a largeish car being driven economically, whereas I'm looking replacing it with a much smaller petrol motor (1.0-1.5L turbo engines) so the diesels would have to beat 4-5L per 100km. 

 

 

 

Edit. Going off Mazda's site

 

Mazda 6 averages 7.0L 100 kms

 

Mazda CX5 diesel 5.7L 100 kms which is pretty good for 4WD. 

 

Doing my annual k's that would mean the diesel would cost about $6133 (with $2480 of RUCS) vs $6616 for petrol. 

 

 

 

Edit. Scrap that. RUCS have gone up!


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  Reply # 2109072 16-Oct-2018 19:37
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mudguard:

MileHighKiwi: The rising cost of petrol is one of the main reasons we recently bought a diesel (2014 Mazda CX-5 2.2L turbo diesel). $85 to fill up compared to $130 in our Mazda 6 (95 petrol). Even with RUC I estimate we'll be about $1k better off per year.


 


It will be interesting to see how you get on. I've been doing my maths on diesel vs petrol and basically need the diesel to be about 0.5L better per 100km to cost less than my current car. That doesn't take into account servicing however. 


And in theory diesels tend to get closer to their stated mileage than petrol. However my comparisons are on a largeish car being driven economically, whereas I'm looking replacing it with a much smaller petrol motor (1.0-1.5L turbo engines) so the diesels would have to beat 4-5L per 100km. 


 


Edit. Going off Mazda's site


Mazda 6 averages 7.0L 100 kms


Mazda CX5 diesel 5.7L 100 kms which is pretty good for 4WD. 


Doing my annual k's that would mean the diesel would cost about $6133 (with $2480 of RUCS) vs $6616 for petrol. 


 


Edit. Scrap that. RUCS have gone up!



How many k's do you do?

My initial calculation was based off the average k's done over the last 9 years in the Mazda 6, which were pretty high. Driving from Upper Hutt to Wellington return daily for 5 years didn't help (68 k per day). Nowdays the CX-5 travels a 22k round trip daily. Our other car (Hyundai Getz) travels about 2 k per day, from home to the train station. We've only had the new car a few days....I'll be monitoring fuel efficiency closely.


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  Reply # 2109097 16-Oct-2018 20:10
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Biggest thing I have found diesel Vs petrol. Is that diesels use far less fuel while idling. So the average distance I can drive on a tank of diesel is similar even comparing mostly open road driving Vs rush hour traffic driving. And of course the RUC cost to drive a given route is always the same, regardless of traffic.

And if you are buying brand new, diesels tend to hold their value better than petrol.

Except modern diesels need regular runs at motorway speed to clean out the particulate filters. And some diesels struggle to warm up when they are just idling or only been driven slowly. Which is a pain during winter. But at least you don't have to pay road tax just to use the aircon during summer.





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  Reply # 2109135 16-Oct-2018 21:44
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Aredwood: Biggest thing I have found diesel Vs petrol. Is that diesels use far less fuel while idling. So the average distance I can drive on a tank of diesel is similar even comparing mostly open road driving Vs rush hour traffic driving. And of course the RUC cost to drive a given route is always the same, regardless of traffic.

And if you are buying brand new, diesels tend to hold their value better than petrol.

Except modern diesels need regular runs at motorway speed to clean out the particulate filters. And some diesels struggle to warm up when they are just idling or only been driven slowly. Which is a pain during winter. But at least you don't have to pay road tax just to use the aircon during summer.

 

 

 

Not much experience of diesels outside the world of Land Rover, but within that use, the diesels tend to need much more servicing at greater cost compared to petrols. The twin turbo engines are renowned for blowing the turbos too, which is an expensive repair. That can offset quite a chunk of fuel saving.

 

 

 

OTOH I did have a diesel Passat wagon (2003MY) as a company car for a year or so from new and that was a fabulous car to drive.






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  Reply # 2109162 16-Oct-2018 22:43
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mudguard:

 

frednz:

 

You would think that with the high price of petrol that people would drive a little bit slower and at least within the speed limits. I was driving at the speed limit the other day and two vehicles ripped past me going about 10kmh over the limit and using a lot more petrol to cover the same distance!

 

 

Depends if your time is more valuable than fuel. I spend 20 hours a week in the car. If someone wants to drive at 85kmh that's fine. But I don't, so let me past!

 

 

Carbon emissions go up too as you use more fuel to cover the same distance. Your kids and theirs...(and theirs and theirs.....) will know who to..... ̶b̶l̶a̶m̶e̶.......thank. 

Amazing people can't keep this in view. It matters more than almost any other thing they will do in their life.....in terms of long term consequences. 





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  Reply # 2109184 17-Oct-2018 00:43
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Linuxluver:

mudguard:


frednz:


You would think that with the high price of petrol that people would drive a little bit slower and at least within the speed limits. I was driving at the speed limit the other day and two vehicles ripped past me going about 10kmh over the limit and using a lot more petrol to cover the same distance!



Depends if your time is more valuable than fuel. I spend 20 hours a week in the car. If someone wants to drive at 85kmh that's fine. But I don't, so let me past!



Carbon emissions go up too as you use more fuel to cover the same distance. Your kids and theirs...(and theirs and theirs.....) will know who to..... ̶b̶l̶a̶m̶e̶.......thank. 

Amazing people can't keep this in view. It matters more than almost any other thing they will do in their life.....in terms of long term consequences. 



Sorry @Linuxluver But it is hard to get motivation to make personal sacrifices to help reduce carbon emissions. When Labour and Green MPs spent in total $1,019,440+GST on air travel in the year to June. At least some of that would have been domestic air travel. Where they could have taken the bus or train instead.

Even better, they could have just driven EVs wherever they needed to go within NZ. And most of their international travel could have been replaced by appearing via video links instead. After all, You have personally proved that you can drive a Nissan leaf almost anywhere in NZ

The money that they spent on air travel. Could have paid for 4 brand new, fully optioned Tesla Model X SUVs. And the change would buy 2 Hyundai Kona EVs. But the goal of reducing their carbon footprint seems to have disappeared as soon as those MPs got access to free air travel paid for by long suffering taxpayers. It also annoys me, that some of my income goes to pay my taxes. Meaning I can't use that money to reduce my own carbon footprint. Only to see them send that money up in smoke (carbon emissions). And then they say that I need to reduce my own emissions more, just to offset their emissions.

Sure, the National party also spent heaps on air travel. But at least they don't brand themselves as an environmental party.





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  Reply # 2109213 17-Oct-2018 07:17
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Aredwood:

 

Sorry @Linuxluver But it is hard to get motivation to make personal sacrifices to help reduce carbon emissions. When Labour and Green MPs spent in total $1,019,440+GST on air travel in the year to June. At least some of that would have been domestic air travel. Where they could have taken the bus or train instead.

 

 

 

Where are you getting that figure from? Unless I'm reading it very wrong, Labour spent $281,464 on air and $347,663 on surface travel, and the Greens spent $64,092 on air and $31,866 on surface travel in the year to June, for a total of $725,085. Figures here and here. Are you including accommodation in that $1M figure? I can get close to your number by adding Wellington accommodation only to all travel total ($1,029,154) but I can't see how you got it exactly.

 

I grant that it's interesting the Greens spent more on air than surface travel, while for Labour it was the other way around, but I didn't check where all those MPs lived. We'd all scream about MPs wasting time not doing things for taxpayers if the MPs for Northland and Southland had to get to Wellington via surface travel every fortnight.

 

In the end it's not a very fair comparison. 99% of people don't live 1000km from where they work, and those that do, fly to get there. I know this because I used to be one of them.

 

FWIW though I think the government should be getting rid of the BMW 7-series and moving to EVs instead. Buy the Jaguar e-Pace, and you've still got an expensive luxury car, but now it's an EV.





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  Reply # 2109223 17-Oct-2018 07:58
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Those links are only to 3 monthly figures. So I had to add up 4 of them to get the annual figures. I also did not include the accommodation figures.

For most people, they are expected to make their own travel arrangements to get to work. Which means that if they live 1000KM away from work, they either have to personally spend their own money on airfares, move closer to work, or just drive.

My understanding is that out of Wellington MPs are also entitled to claim the costs of renting a house in Wellington. So they can just live local to their work. Instead of needing to do very long distance commuting.





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  Reply # 2109239 17-Oct-2018 08:18
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Aredwood: Those links are only to 3 monthly figures. So I had to add up 4 of them to get the annual figures. I also did not include the accommodation figures.

 

 

 

 

Ah, I see we have different definitions of what 'Year to June' means, but ok.

 

 

 



Which means that if they live 1000KM away from work, they either have to personally spend their own money on airfares, move closer to work, or just drive.

 

 

 

Having, as I said, been one of those people for 5 years, I assure you I did not spend my own money on airfares, taxis, or accommodation. I drove from Sydney to Melbourne a couple of times, but that was mostly because the mileage cost the company about the same as airfare (and I promised not to use taxis while there) but the money went into my pocket rather than an airline. But for all other travel, I flew, and the company paid.

 

And when I say 'one of those people' I mean that other employees in my office could be hired, work out their contract, and leave without ever meeting me in person as I was in the office for a total of about 2 weeks across a whole year.

 

 





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  Reply # 2109499 17-Oct-2018 10:41
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MileHighKiwi: >How many k's do you do?

My initial calculation was based off the average k's done over the last 9 years in the Mazda 6, which were pretty high. Driving from Upper Hutt to Wellington return daily for 5 years didn't help (68 k per day). Nowdays the CX-5 travels a 22k round trip daily. Our other car (Hyundai Getz) travels about 2 k per day, from home to the train station. We've only had the new car a few days....I'll be monitoring fuel efficiency closely.



I did a bit over 40,000 last year, it will higher this year.

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  Reply # 2109617 17-Oct-2018 12:09
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Geektastic:

 

Not much experience of diesels outside the world of Land Rover, but within that use, the diesels tend to need much more servicing at greater cost compared to petrols. The twin turbo engines are renowned for blowing the turbos too, which is an expensive repair. That can offset quite a chunk of fuel saving.

 

OTOH I did have a diesel Passat wagon (2003MY) as a company car for a year or so from new and that was a fabulous car to drive.

 

 

That's mainly sorted these days, I think the maximum service interval (oil/filter change) on my diesel is 20,000km - but it self monitors and adjusts based on duty cycle and displays that on the trip computer, so could be less, but nothing like the 5,000km oil change required on the diesel it replaced.

 

I'm not sure on (progressive) twin-turbo, but in general turbos aren't the problem they used to be - what used to be an expectation that a turbo unit would fail at ~100,000km doesn't seem to be happening these days, I don't know of anybody who's had to replace a turbo in a modern diesel - despite some of them doing high mileage. 

 

I think the twin turbos are mainly the result of European emission laws, they use a small engine with very high boost to meet CO2 emission levels in test, and you end up with a lot of hesitation and turbo-lag, so they run one low pressure turbo to provide continuous boost in normal operation, and the second higher pressure turbo kicks in with less fuss.

 

The service item which is causing issues is the diesel particulate filter, some models seem to have frequent issues, and all models will have issues if they're only used for around-town use and not run at highway speed / longer duration when required.  If the DPF dies, then OEM replacements are extremely expensive.  If you didn't obey the car when it told you that the vehicle needed to be taken for a long run at speed, then you'd void your warranty.  If you do all your running around town with no highway/motorway trips, then any new diesel probably isn't a great idea.

 

New cars are going to have to be fitted with particulate filters.  The makers are saying that these won't cause any issues - which is exactly what you'd expect them to say.

 

I understand that aftermarket DPF are available at a fraction of OEM prices - also not surprising.


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